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Abstract:
Physiological studies in macaques have revealed that cortical
area V4 is important for the perception of color and form
information. V4 lesions typically produce pronounced form deficits
and more mild color deficits. Conversely, humans with V4 lesions
generally exhibit severe achromatopsia but relatively preserved
form perception. The goal of the present study was to
systematically examine form perception in a patient with left
hemiachromatopsia, due to a small right occipito-temporal (V4)
infarct. Patient A.R. performed a series of discrimination tasks in
his right and left visual fields. A staircase procedure was used to
simultaneously obtain discrimination thresholds in each hemifield.
A.R.'s performance for motion and very simple form stimuli was
normal. However, he showed marked impairments in the discrimination
of complex forms, including non-Cartesian (curvature) stimuli and
second-order textures. Additional tests used a variety of form
vision tasks previously conducted in animals with V4 lesions. In
all, results were consistent with those obtained with animals. We
conclude that, in regard to form vision, human V4 is functionally
equivalent to the corresponding area in macaques.
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